div.c

一款类linux的操作系统源码

#include <stdlib.h>		       /* div_t */

div_t
div(int num, int denom)
{
    div_t r;

    r.quot = num / denom;
    r.rem = num % denom;
    /* 
     * The ANSI standard says that |r.quot| <= |n/d|, where n/d is to be
     * computed in infinite precision.  In other words, we should always
     * truncate the quotient towards 0, never -infinity.
     * 
     * Machine division and remainer may work either way when one or both of n
     * or d is negative.  If only one is negative and r.quot has been
     * truncated towards -inf, r.rem will have the same sign as denom and the
     * opposite sign of num; if both are negative and r.quot has been
     * truncated towards -inf, r.rem will be positive (will have the opposite
     * sign of num).  These are considered `wrong'.
     * 
     * If both are num and denom are positive, r will always be positive.
     * 
     * This all boils down to: if num >= 0, but r.rem < 0, we got the wrong
     * answer. In that case, to get the right answer, add 1 to r.quot and
     * subtract denom from r.rem.
     */
    if (num >= 0 && r.rem < 0) {
	r.quot++;
	r.rem -= denom;
    }
    return r;
}